In 2005, the YZ250 received a new lightweight aluminum frame. For 2006 the YZ250 has received a number of detail improvements that continue to give it the edge in MX1 competition. The world’s lightest aluminum frame is now complimented by a new “hydro formed” swingarm. The twin chamber 48mm fork has been revised and the rear shock utilizes a trick titanium spring. We even made the Renthal handlebar adjustable.

Engine:

Liquid-cooled, 249cc, piston-reed-valve-inducted, 2-stroke engine is lightweight and compact. Its reputation for exceptionally broad, hard-hitting powerband will continue for 2006.

The cylinder feature a ceramic composite coating which insures uniform heat dissipation, reduced friction and a longer service life.

For 2006, the cylinder exterior is painted with silver paint for a more attractive appearance.

YZ250-spec YPVS power valve system features a total of three slides (one main and two auxiliary slides) which provides the benefits of both solid, low rpm power delivery and a strong top-end punch. The YPVS system varies the exhaust port height and timing based on engine rpm. The valves are also designed to match the curvature of the cylinder resulting in a strong seal, thereby providing increased power delivery.

38mm Keihin PWK carburetor with power jet and throttle position sensor (TPS) ensures precise fuel/air mixing and extra-crisp throttle response throughout the powerband.

Computer designed expansion chamber provides maximum engine performance while the lightweight, aluminum silencer is rebuildable, so performance can be maintained at the optimum level and noise levels can be controlled.

Trick, works-style clutch lever features a race-spec “barrel adjuster” for on-the-fly adjustability. There is a new, larger boot covering the adjuster that provides more grip for easier operation.

Chassis/Suspension:

Aluminum, semi-double-cradle style frame was a completely new design in 2005. The obvious benefit of an aluminum frame is a significant reduction in overall machine weight. Yamaha has maintained the semi-double cradle design because it offers an excellent balance between stiff lateral and torsion rigidity while offering more controlled flex in the longitudinal plane. This frame design offers the ideal “stiffness balance” which means it offers the flexibility of a steel frame with the light weight of an aluminum frame. Over the years, the “knock” on aluminum frames is that they were too stiff and therefore make suspension set-up difficult and may provide a harsh ride. This frame is made from a unique mix of castings, forgings and extrusions that provide stiffness where it is required and flexibility in other areas. The result is the world’s lightest aluminum MX frame, which provides excellent handling, good ride quality, excellent stability and responsive cornering performance.

New, lightweight, tapered, aluminum swingarm is produced using “hydro forming”, a special forming method that uses high pressure water to form shapes. The new swingarm provides improved overall chassis balance thanks to the addition of re-enforcing ribs in the cast aluminum around the pivot area. The result is a 2% increase in torsional rigidity for improved handling.

New forged lower triple clamp features an increase in longitudinal rigidity which allows greater flexibility to absorb the forces applied between the front fork and the frame for improved handling.

The fork pitch (or separating width between the tubes) has been increased for 2006 for improved handling.

New adjustable handlebar mounts allow the handlebars to be moved 10mm rearward if desired.

New, lighter, improved 48mm, adjustable, inverted, Kayaba cartridge forks feature a revised twin-chamber design. The twin chamber design means the damper unit is in a separate structure which prevents aerated fork oil from entering the inner damper assembly and degrading its damping abilities. Since the inner damper is pressurized, it also eliminates bubbles forming in the oil.

For 2006, the balance between the inner and outer tubes has been optimized, while the Kashima coating on the pressure tank and the piston rod reduce friction for smoother suspension performance. The cylinder diameter has been revised from 25 to 24mm for improved primary cushioning and a low friction oil seal has been used. The weight of the fork assembly has been reduced by 2.5%

The 48mm KYB fork also features a relocated Transfer Control Valve (TCV). The TCV enhances the damping force of the inner damper from mid stroke to full stroke and improves bottoming characteristics. The benefit of TCV is more precise control throughout the full stroke range. For 2006 the TCV is now located on the upside of the spring and its function is controlled by piston speed, not piston position.

The damper rod diameter in the 2006 KYB shock has been increased from 16 to 18mm while sub tank capacity has been increased by 30% for improved shock performance, Kashima coating is used in the shock body and sub tank to reduce friction and improve suspension performance during a long moto.

All new, trick titanium shock spring reduces weight by 500 grams. This is a significant weight reduction since it is unsprung weight that has been reduced. A reduction in “unsprung” weight , causes a dramatic effect on suspension performance. The new titanium spring provides outstanding strength, and durability, combined with reduced weight.

The 2006 Kayaba shock utilizes a full rebound oil lock system for excellent suspension function and great ride quality.

245mm rear disc brake with single piston caliper uses an integrated master cylinder (fluid reservoir is integrated into the top of the master cylinder) for strong stopping power with excellent feel and control.

New rear brake caliper is the same as that found on the 4-stroke models. It not only improves rear braking efficiency but also sits lower on the swingarm to reduce the center of gravity. The new caliper features a new, plastic caliper protector and a 30% lighter lower disc protector.

Specially designed “Sun Star” rear sprocket increases the contact area between the sprocket and chain rollers, thereby reducing the load on the chain and increasing the service life of both chain and sprocket.

New “flat-design” seat features multi density foam that provides good initial softness / comfort and then increases the firmness as more pressure is applied. The seat is raised 10mm for 2006. The “pebble” or “gripper” finish on the top and side surfaces provides excellent rider grip and durability.

New front fender and number plate provide a fresh styling appearance. The seat, handlebar and fuel tank ergonomics provide excellent freedom of movement for the rider.